The present invention relates to a method for the quantitative evaluation of color image signals available from, for example, charge coupled device (CCD) color image sensors fabricated as a semiconductor IC. The invention also pertains to a color image signal evaluating apparatus utilizing the above-mentioned quantitative evaluation method.
In recent years there have been put to practical use CCD color image sensors which have mosaic color filters or stripe color filters coated on their front for creating color image signals. The CCD is produced using semiconductor IC techniques but it may sometimes be defective from various causes in its manufacturing process. Moreover, a positioning error or geometric misalignment is often induced when printing the color filter on the CCD in the fabrication of the color image sensor. Reproducing a color image signal derived from such an image sensor, the picture suffers various color reproduction errors owing to defects of the image sensor itself and geometric misalignment of the color filter. For instance, in the case where monochromatic light with no pattern, such as standard white light, is shed evenly all over the image receiving surface of the image sensor, (1) a slanted pattern of colored stripes appears in the reproduced picture, (2) a colored pattern of vertical or horizontal stripes appears in the reproduced picture, or (3) the reproduced picture is colored over a wide area.
In conventional testing of color image sensors, test personnel visually inspect the picture quality of a display image provided on a CRT display screen based on the color image signal from each image sensor and determine whether or not the above-mentioned color reproduction errors are each within a predetermined limit range. Hence, the traditional quality conformance inspection of color image sensors in the past was inefficient and many test personnel were needed for quality inspection of image sensors at the mass-production site, in particular. Besides, such evaluation of the picture quality is subjective and hence is inevitably subject to an individual checker's judgment as to the afore-mentioned color reproduction errors. This poses a problem that image sensors having passed inspection vary greatly the in their quality as to the color reproduction.